Nice article. This is a great example of how Domain-Driven Design pays off. By really paying attention to how users think of the problem and expressing that in their design, they ended up with a richer domain model which in turn let them get better code and a better user experience.
Thanks! A good UX was indeed one of our main goals and we weren't sure whether we're not overdoing this (again, the Netscape history ;|). But we kept in mind that simpler solutions already exist and it doesn't make sense to just copy them. That'd make the job easier, but we'd end up with the same issues that we identified in the existing platforms (annoying conflict resolution, stability issues, platform limitations to linear content – no tables, no nested blocks). So we risked taking the long path. The UX served as a compass and allowed making some reasonable shortcuts in some non-critical places. If we'd try to solve all possible issues that we've hit, we'd still be in the starting point :D